Dipankar Das, Aritra Roy, Sourav Sutradhar, Felipe Fantuzzi and Biswa Nath Ghosh




The development of simple yet efficient receptors that rapidly detect and monitor amino acids with high sensitivity and reliability is crucial for the early-stage identification of various diseases. In this work, we report the synthesis and characterisation of a copper(II) complex, CuCl2L, by employing a 2,6-dipyrazinylpyridine (dppy)-based ligand (L = 2,2’-(4-(3,4,5-trimethoxyphenyl)pyridine-2,6-diyl)dipyrazine). The in-situ prepared CuCl2L receptor exhibits an instantaneous response to the presence of L-Cysteine (Cys) and L-Histidine (His) in aqueous acetonitrile (4:1 v/v, 10 mM HEPES buffer, pH 7.4). Furthermore, competitive experiments demonstrate the selectivity of CuCl2L towards Cys (1 equiv.) in the vicinity of other L-amino acids in the aforementioned solvent conditions. The lowest detection limits for Cys and His are calculated as 0.33 µM and 1.40 µM, respectively. DFT calculations offer a plausible explanation for the observed selectivity of the CuCl2L receptor towards Cys and His. They reveal that the most stable conformer of Cu:Cys complex (1:1) is a five-membered ring formed through N,S-coordination mode (ΔG = –26.7 kcal mol–1) over various other possible coordination modes, while comparable ΔG values are only obtained for Cu:His complexes featuring two His moieties.